On Mon, 24 Sep 2007 16:12:19 +0530 Balbir Singh
<[email protected]> wrote:
> Peter Zijlstra wrote:
> >
> > Just an idea I had, it seems like a good idea to wait for RCU callbacks
> > in reclaim so that we won't get all of memory stuck there.
> >
> > If this location is too aggressive we might stick it next to
> > disable_swap_token().
> >
> > ---
> > Couple RCU and reclaim.
> >
> > There could be a lot of memory stuck in RCU callbacks. Wait for RCU to
> > finish before giving it another go.
> >
> > Placed in kswapd and not direct reclaim path because kswapd never holds
> > rcu_read_lock() at this point and can thus not deadlock. Direct reclaim
> > callers might hold rcu_read_lock() and would suffer from deadlocks if
> > sync_rcu() were to be called.
> >
> > Signed-off-by: Peter Zijlstra <[email protected]>
> > ---
> > mm/vmscan.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > Index: linux-2.6/mm/vmscan.c
> > ===================================================================
> > --- linux-2.6.orig/mm/vmscan.c
> > +++ linux-2.6/mm/vmscan.c
> > @@ -1435,8 +1435,10 @@ loop_again:
> > unsigned long lru_pages = 0;
> >
> > /* The swap token gets in the way of swapout... */
> > - if (!priority)
> > + if (!priority) {
> > + synchronize_rcu();
Bah, it seems I send the wrong patch out :-/
this is the one against disable_swap_token(). I meant to send out this
one:
@@ -1527,8 +1527,10 @@ loop_again:
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
*/
- if (total_scanned && priority < DEF_PRIORITY - 2)
+ if (total_scanned && priority < DEF_PRIORITY - 2) {
+ synchronize_rcu();
congestion_wait(WRITE, HZ/10);
+ }
> Interesting change
>
> 1. I suspect that synchronize_rcu() is most likely to free up
> slab pages, so shrink_slab() will clean up all the freed
> pages. Could we add a comment to indicate the same?
Yes indeed, will add such a comment.
> 2. Shouldn't we do this in balance_pgdat() as well?
Uhm, this is balance_pgdat() (both these changes) :-)
Only kswapd can do this, direct reclaim has deadlock potential.
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